In the past, leaded petrol was an important source of lead, but is less so today due to the transition to unleaded petrol. Lead was also a common ingredient in paint, and was a problem due to industry and lead water pipes. Today, lead ammunition is the most important source of harmful discharges, but total discharges of lead have been reduced by around 80 per cent in the past ten years.
Lead affects our nervous system and can lead to impaired learning ability. Lead can cause foetal injury and have an adverse effect on fertility. Children are extra sensitive to lead because they absorb more lead than adults. Lead also affects enzyme activity in the blood and the transport of oxygen around our bodies. It also accumulates in our bones.
The most important sources of lead in our diet are grain products, dairy products and vegetables. Lead is absorbed to some extent by shellfish, whereas fish only absorb lead to a limited extent in fillets. Seafood is therefore a very limited source of lead in our diet. The maximum level for lead content in the edible part of fish is 0.3 mg/kg. The levels in fish fillets are mostly so low that they cannot be detected with today’s sensitive analysis methods (the levels are below the limit of quantification). No tolerable weekly intake is presently valid for lead.
Maximum levels in fish feed
Only limited amounts of lead occur in fish feed. The average levels are around 0.09 mg lead per kg feed, whereas the maximum level for lead in fish feed is 5 mg/kg. Very little is transferred to the fish, and the levels are mostly below the limit of determination in fish fillets. More lead is transferred from the feed to the environment than to the fish, as fish do not absorb lead. However, discharges to the environment are limited due to the low levels of lead in the feed. Nor does it have an effect on fish health.